The present invention relates to a device for the supply of a mixture of air and fuel to the manifold of an internal combustion engine, of the type which includes an electromagnetically operated fuel atomisation and metering valve operable to deliver predetermined quantities of fuel in the form of atomised particles.
As is known, devices of this type normally include several parts within which are formed a duct which puts an air intake opening into communication with a mixture supply opening the flow cross section of which is controlled by a butterfly valve; the fuel atomisation and metering valve is able to deliver atomised fuel into the air which flows along the said duct in such a way as to form with this a mixture of air and atomised fuel.
Devices of the type described normally include a flange able to allow them to be fixed to an attachment plate of the manifold, and are normally provided with an air filter operable to filter the air which enters into the air intake of the device.
Devices of the type described have various disadvantages.
First of all, they are not able to prepare a perfectly homogeneous mixture of air and fuel in all operating conditions of the device; this is due to the fact that along the duct into which the atomised fuel is delivered, the path of the air is such as not always to give rise to sufficient vortex movements for homogeneous mixture with the fuel particles. Moreover, along the said duct, within which both the air and the mixture of air and fuel moves, there is the tendency for the formation of fuel droplets, with the disadvantage of producing an irregular operation of the engine when idling, and of dissipating part of the energy provided by the atomisation and metering valve in the step of atomisation of the fuel; in fact, the flow of atomised fuel which is delivered from the atomisation and metering valve can be perturbed by the flow of air and directed onto the surfaces of the duct and those of the butterfly valve, giving rise in this way to droplets of fuel on these surfaces; these, passing in a discontinuous manner through the mixture delivery outlet cause anomalous operation, particularly in slow running conditions.
In devices of the type described, during the movement of the air and mixture along the first mentioned duct, there are pressure losses due to the form of the duct itself and the high aerodynamic resistance which opposes the movement of the fluid and which is generated by parts and members of the device. Further the flow of mixture which leaves the first mentioned mixture delivery outlet can be non-uniform with the disadvantage of giving rise to irregularities in metering to the various cylinders; different distributions of the flow of mixture to the various cylinders is also encountered depending on whether a filter is mounted on the device or whether it has no filter.
Devices of the type indicated are structurally rather complex because of the numerous parts of which they are made and the manner in which the parts are connected together; moreover, they are rather cumbersome which makes it particularly difficult to replace a conventional carburetor with a device of the type described on an internal combustion engine.
Normally, devices of this type can be mounted directly on the plate of the manifold on which a traditional carburetor is mounted, but it is necessary to utilise suitable connector parts and members; for fixing the device to the said plate rather complicated connection members must be utilised, which therefore makes the said assembly and dismantling operations of the device itself from the first mentioned plate rather difficult.
Finally, because of the form of the air induction opening, filters of particular, and sometimes rather complex, form are required in the forward parts.